<p> September 14th - Microphone design considerations; Mic Preamps Note: Pg.1 was to be presented in the afternoon class, pgs 2+3 in the evening, but they have been combined because we ran out of time this afternoon</p><p>Level & Impedance Mic level ~5-50 mV, 50-200 Ohm (low) impedance Instrument Level ~50mV - 1 V 15,000 Ohm (high) impedance Line level ~50mV - 2 V 100-1500 Ohm impedance Speaker level ~50-100 V 4-16 Ohm impedance More on levels</p><p>How do we match all these disparate levels? Mics/Instruments go into preamps, which boost the signal to line level then Line level devices go into power amps then Power amps go into speakers then Boom goes the dynamite</p><p>How do we match all these disparate impedances? Bridging Setup = input impedance should always be at least 10x source impedance -to help avoid loss in level -to help avoid cables impedance lending a significant impact -e.g.: mic preamp inputs are usually around 1500 ohm to match the 50-200 ohm output of microphones</p><p>Some vintage equipment doesn’t play along. Everything used to be matched to 600 ohms (except power amplifier outputs and speakers)</p><p>What does that sound like when you attach vintage equipment to modern devices? -impedance changes depending on frequency, so frequency response will change -output level from the source will be affected -this means we’ll have to turn the preamp up more, and that means MORE NOISE Polar Patterns  Measurement & Variables  Proximity Effect http://www.soundonsound.com/sos/sep00/articles/direction.htm</p><p>Different types of designs and construction methods  Dynamic diaphragms, housings, schematics and intended uses  Ribbon diaphragms, housings, schematics and intended uses & hazards  Condenser diaphragms, housings, schematics and intended uses</p><p>Additional considerations  Diaphragm o Small o Large o Single-element o Dual-element  Directionality o Proximity Effect  Housing  Windscreen/Headbasket o Pop filters o Reflexion filters o Anything near a microphone will color the sound of a microphone . Remember the music stand!  Electronics o Transformer vs. transformerless  What is it’s intended purpose?  Durability</p><p>Microphone Specifications  Variables in impedance and measurement  Frequency response  Self noise  Sensitivity  ‘Max’ SPL</p><p>Comparing microphones quantitatively and qualitatively  Recordinghacks.com  bradfordswanson.com/mic  3Daudioinc.com Mic Preamps Preamp specifications  Impedance o What load is presented to the microphone? o Should be at least 10x the impedance of the microphone . Mismatched impedance = drop in level and some effect to frequency response  Noise (Equivalent Input Noise) o How much noise does the preamp introduce on its own? o Should be less than -110 dB  Maximum Gain o How much amplification can the preamp provide? o Should be at least 60 dB . Might need to engage the pad to acheive this  Maximum Input Level o How much input can the preamp receive from the source before distorting? o Should be around +4 dBu (professional line level) . Might need to engage the pad to achieve this  Distortion o THD+N (Total Harmonic Distortion plus Noise) o How much distortion does the preamp introduce at MIL?</p><p>Biasing for high-gain/low-noise  Preamps are usually the noisiest part of your signal chain because they are amplifying a very small signal by a significant amount o And they are amplifying after a series of resistors, which are subject to thermal noise (unless your recording in absolute zero)  For lower noise, we apply DC bias to the circuit o Adjust resistors on the bias circuit, listen to output, tweak ‘til the noise is lowest  Transistor tolerances and durability. Temperature is a thing!  More information</p><p>Preamp Specs & Schematics  Yamaha O1V96  http://www.gyraf.dk/schematics/schematics.html  http://www.jensen-transformers.com/schematics/  Benchmark/Burdick/Cohen History of the Active Mic Preamp </p>